Audio system



FIG. 1 is a perspective view of an audio system as seen from the front, top and left side;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a right side view thereof.

The dotted line portions of the drawings represent environmental structure only and do not form part of the claimed design. 

The ornamental design for an audio system, substantially as shown and described. 